Go to Settings > Accessibility > Text size to increase the weight, or search for "Adjust ClearType text" to improve font rendering and sharpness.
You can enable Dark Mode by holding the brightness slider in the Control Center and tapping the Dark Mode icon. Help with Text Color Changing in Dark Mode on Mobile klea dark
If the text currently appears gray or a lighter shade, you can manually set it to pure black ( #000000 ). Go to Settings > Accessibility > Text size